Generally, in order to use a battery as a power source, it is necessary to be aware of available power of the battery under a specific condition. In particular, in a hybrid electric vehicle that uses the battery as one of its power sources, it is important to exactly predict a maximum available power of the battery. However, the available power of the battery changes according to a state of charge (SOC), a battery temperature, and aging of the battery. Therefore, it is difficult to exactly know the available power of the battery.
A battery control unit for a hybrid electric vehicle generally determines available charge power and available discharge power in real time, and sends the determined available power information to a hybrid electric vehicle control unit (HCU), in order to maximally use the battery. In the past, the available battery power has generally been calculated using a condition of maximum electric power transmission. As an example, in a steady state, battery power can be calculated by the following equation.
                              P          max                =                                            R              e                        ⁢                          I              t              2                                =                                    R              e                        ×                                          (                                  Voc                                      r                    +                                          R                      e                                                                      )                            2                                                          [        Equation        ]            
where Re is an equivalent resistance of a battery, Voc is an effective no-load voltage of the battery, and r is a resistance of a load.
In the above equation, if the equivalent resistance of the battery is equal to the resistance of the battery (i.e., r=Re), a maximum power (i.e., Pmax=Voc2/4Re) is transmitted to the load. That is, a maximum power can be used when the equivalent resistance of the battery is equal to the resistance of the battery from the condition of the maximum power transmission. However, in the above method to calculate the maximum available power, battery operating voltage is not considered, and the resistance of the load must be known to calculate the maximum power. Therefore, it is quite difficult to use such a method for a hybrid electric vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.